108 research outputs found
Precision measurements with polar molecules: the role of the black body radiation
In the perspective of the outstanding developments of high-precision
measurements of fundamental constants using polar molecules related to ultimate
checks of fundamental theories, we investigate the possibly counterproductive
role of black-body radiation on a series of diatomic molecules which would be
trapped and observed for long durations. We show that the absorption of
black-body radiation at room temperature may indeed limit the lifetime of
trapped molecules prepared in a well-defined quantum state. Several examples
are treated, corresponding to pure rotational absorption, pure vibrational
absorption or both. We also investigate the role of a black-body
radiation-induced energy shift on molecular levels and how it could affect
high-precision frequency measurements
First record of Labena striata Townes and Townes, 1966 (Hymenoptera, Ichneumonidae, Labeninae) from Colombia
Precision bond lengths for Rydberg Matter clusters KN (N = 19, 37, 61 and 91) in excitation levels n = 4 - 8 from rotational radio-frequency emission spectra
Clusters of the electronically excited condensed matter Rydberg Matter (RM)
are planar and six-fold symmetric with magic numbers N = 7, 19, 37, 61 and 91.
The bond distances in the clusters are known with a precision of +- 5% both
from theory and Coulomb explosion experiments. Long series of up to 40
consecutive lines from rotational transitions in such clusters are now observed
in emission in the radio-frequency range 7-90 MHz. The clusters are produced in
five different vacuum chambers equipped with RM emitters. The most prominent
series with B = 0.9292 +- 0.0001 MHz agrees accurately with expectation (within
2%) for the planar six-fold symmetric cluster K19 in excitation level n = 4.
Other long series agree even better with K19 at n = 5 and 6. The ratio between
the interatomic distance and the theoretical electron orbit radius (the
dimensional ratio) for K19 in n = 4 is found to be 2.8470 +- 0.0003. For
clusters K19 (n = 6) and K37 (n = 7 and 8) the dimensional ratio 2.90 is the
highest value that is found, which happens to be exactly the theoretical value.
Clusters K61 and K91 in n = 5 and 6 have slightly lower dimensional ratios.
This is expected since the edge effects are smaller. Intensity alternations are
observed of approximately 7:3. The nuclear spins interact strongly with the
magnetic field from the orbiting electrons. Spin transitions are observed with
energy differences corresponding accurately (within 0.6%) to transitions with
apparent total (delta)F = -3 at excitation levels n = 5 and 6. The angular
momentum coupling schemes in the clusters are complex but well understood.Comment: 37 pages, 14 figure
The Supermassive Black Hole at the Galactic Center
The inner few parsecs at the Galactic Center have come under intense scrutiny
in recent years, in part due to the exciting broad-band observations of this
region, but also because of the growing interest from theorists motivated to
study the physics of black hole accretion, magnetized gas dynamics and unusual
star formation. The Galactic Center is now known to contain arguably the most
compelling supermassive black hole candidate, weighing in at a little over 2.6
million suns. Its interaction with the nearby environment, comprised of
clusters of evolved and young stars, a molecular dusty ring, ionized gas
streamers, diffuse hot gas, and a hypernova remnant, is providing a wealth of
accretion phenomenology and high-energy processes for detailed modeling. In
this review, we summarize the latest observational results, and focus on the
physical interpretation of the most intriguing object in this region---the
compact radio source Sgr A*, thought to be the radiative manifestation of the
supermassive black hole.Comment: Annual Review of Astronomy & Astrophysics, Vol. 39 (2001), in press,
48 pages, 20 figures (partially in reduced quality), also available at
http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#gcrevie
Line-shape transition of collision broadened lines
Using the newly developed technique of THz time-domain spectroscopy, we have measured the far-wing absorption line profile of the ensemble of collision broadened ground state rotational lines of methylchloride vapor out to more than 200 linewidths from resonance, corresponding to frequency offsets as much as 5X the resonant frequency. On these far wings the measured absorption is approximately an order of magnitude less than that predicted by the van Vleck-Weisskopf theory. Our observations show that at higher frequencies a transition occurs from the regime of the van Vleck- Weisskopf theory to the regime of the Lorentz theory.Peer reviewedElectrical and Computer Engineerin
Human Alpha Defensin 5 Expression in the Human Kidney and Urinary Tract
The mechanisms that maintain sterility in the urinary tract are incompletely understood. Recent studies have implicated the importance of antimicrobial peptides (AMP) in protecting the urinary tract from infection. Here, we characterize the expression and relevance of the AMP human alpha-defensin 5 (HD5) in the human kidney and urinary tract in normal and infected subjects.Using RNA isolated from human kidney, ureter, and bladder tissue, we performed quantitative real-time PCR to show that DEFA5, the gene encoding HD5, is constitutively expressed throughout the urinary tract. With pyelonephritis, DEFA5 expression significantly increased in the kidney. Using immunoblot analysis, HD5 production also increased with pyelonephritis. Immunostaining localized HD5 to the urothelium of the bladder and ureter. In the kidney, HD5 was primarily produced in the distal nephron and collecting tubules. Using immunoblot and ELISA assays, HD5 was not routinely detected in non-infected human urine samples while mean urinary HD5 production increased with E.coli urinary tract infection.DEFA5 is expressed throughout the urinary tract in non-infected subjects. Specifically, HD5 is expressed throughout the urothelium of the lower urinary tract and in the collecting tubules of the kidney. With infection, HD5 expression increases in the kidney and levels become detectable in the urine. To our knowledge, our findings represent the first to quantitate HD5 expression and production in the human kidney. Moreover, this is the first report to detect the presence of HD5 in infected urine samples. Our results suggest that HD5 may have an important role in maintaining urinary tract sterility
Interferometric Observations of Rapidly Rotating Stars
Optical interferometry provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Through direct observation of
rotationally distorted photospheres at sub-milliarcsecond scales, we are now
able to characterize latitude dependencies of stellar radius, temperature
structure, and even energy transport. These detailed new views of stars are
leading to revised thinking in a broad array of associated topics, such as
spectroscopy, stellar evolution, and exoplanet detection. As newly advanced
techniques and instrumentation mature, this topic in astronomy is poised to
greatly expand in depth and influence.Comment: Accepted for publication in A&AR
Linking the thermodynamic temperature to an optical frequency: recent advances in Doppler broadening thermometry
- …